As LED lighting becomes more and more intelligent the demand for lighting control and scene lighting is becoming stronger and stronger. At present, there are more and more dimming power supply products on the market. In the existing phase-cutting constant voltage dimming power supply, a switching tube is usually added to control the on/off of the output, so as to realize the change of the average value of the output current. When the output is short-circuited, the switching tube enters the variable resistance area. At this time, the switching tube is subjected to relatively large power, and as time passes, the temperature will accumulate, eventually causing the outer casing to melt and cause a fire. Therefore, the protection of the output short circuit is an important issue in the dimming power supply, directly related to the safety of its use. At present, the output short circuit or overcurrent protection adopts a self-recovery fuse or a temperature switch. The response speed in this method is relatively slow, and the LED constant voltage dimmer is often burned out, and the service life is shortened.